Sodium and water accumulation in an injured cell are a direct result of:

Choice A Reason:

Administering the drug at intervals longer than the drug half-life is not typically recommended for medications with a narrow therapeutic range. These drugs require precise dosing to maintain therapeutic levels without reaching toxic levels. Extending the dosing interval could lead to subtherapeutic levels, reducing the drug’s effectiveness.

Choice B Reason:

Teaching the patient that maximum drug effects will occur within a short period is not specific to drugs with a narrow therapeutic range. While some medications may have rapid onset of action, the critical aspect of narrow therapeutic range drugs is maintaining consistent blood levels to avoid toxicity or subtherapeutic effects.

Choice C Reason:

Administering the medication intravenously is not a requirement for all drugs with a narrow therapeutic range. While IV administration can provide precise control over drug levels, many narrow therapeutic range drugs can be administered orally or through other routes. The key is monitoring and adjusting the dose based on blood levels.

Choice D Reason:

Ordering lab tests to check blood drug levels is essential for managing medications with a narrow therapeutic range. These drugs have a small margin between therapeutic and toxic doses, so regular monitoring of blood levels helps ensure the drug remains within the safe and effective range. This practice is known as therapeutic drug monitoring (TDM) and is crucial for drugs like warfarin, phenytoin, and digoxin.

Choice A Reason:

To determine how much of the medication remains in the body after a certain period, we need to understand the concept of half-life. The half-life of a medication is the time it takes for the concentration of the drug in the bloodstream to reduce by half. For Medication A, the half-life is 3 hours. After 12 hours, which is four half-lives, the amount of medication remaining can be calculated step by step.

Choice B Reason:

Let’s break down the calculation. Initially, the patient receives 400 mg of Medication A. After the first half-life (3 hours), the amount of medication remaining is 400 mg ÷ 2 = 200 mg. After the second half-life (6 hours), the amount remaining is 200 mg ÷ 2 = 100 mg. After the third half-life (9 hours), the amount remaining is 100 mg ÷ 2 = 50 mg. Finally, after the fourth half-life (12 hours), the amount remaining is 50 mg ÷ 2 = 25 mg. Therefore, 375 mg is not a correct answer.

Choice C Reason:

Similarly, 150 mg is not correct. As shown in the detailed calculation, the amount of medication decreases by half every 3 hours. After 12 hours, the remaining amount is 25 mg, not 150 mg. This choice does not align with the half-life calculation.

Choice D Reason:

This is the correct answer. The step-by-step calculation shows that after 12 hours, which is equivalent to four half-lives, the amount of Medication A remaining in the patient’s body is 25 mg. This demonstrates the principle of half-life and how the concentration of a drug decreases over time.